During brain injury, the brain is deprived of freshly oxygenated blood. Following this, neurons in the brain die soon after or at a later stage occurring hours to days after the insult and are not capable of regeneration. Glial cells, which are non-neuronal cells essential for normal brain functioning, also die. Permanent loss of function is a likely outcome of a severe injury to the brain.
Perinatal hypoxic-ischemic injury continues to be a major cause of death or later neurodevelopmental sequelae. This type of head injury in the neonate occurs during asphyxial, traumatic, toxic, infectious, metabolic, ischemic or hypoxic insults to the brain. Specifically, perinatal asphyxia caused by cord occlusion or associated with intrauterine growth retardation; perinatal asphyxia associated with failure of adequate resuscitation or respiration; near miss drowning, near miss cot death, carbon monoxide poisoning, ammonia or other gaseous intoxication, coma, hypoglycaemia and status epileptics; stroke; cerebral trauma. Experimental and clinical studies have shown that hypoxic ischemic encephalopathy (HIE) is an evolving process. Following the primary phase of energy failure during asphyxia cerebral metabolism may initially recover in a latent phase, but then deteriorate in a secondary phase of brain injury 6 to 15 hours later. In the human infant the severity of delayed energy failure after asphyxia is correlated with adverse neurodevelopmental outcome at one and four years of age.
It appears that hypothermic intervention in pathological processes occurring in the brain after brain injury may result in an improved neural outcome (Marion et al., New Eng. J. Med., 336:540-546 (1997)). Experimentally, hypothermic treatment following reperfusion after brain injury has been shown to increase numbers of viable neurons (Gunn et al., J. Clin, Invest, 99:248-256 (1997)).
Hypothermic therapy after brain injury is one method that can be used to rescue neurons and other cells from the phase of delayed brain damage that occurs after reperfusion. It involves cooling the brain tissue to a temperature of 30-34° C. As a consequence, pathological processes leading to delayed neuronal and other cell death are inhibited by as yet unknown mechanism/s.
The adverse consequences of hypothermia and the importance of maintaining newborn infants in the thermoneutral range have been known to pediatricians for the past 40 years, since the classic study by Silverman et al, in which infants 1501 g and more kept in “hypothermic” incubators had temperatures of 34.7±0.7° C. These findings were confirmed in subsequent studies with no cause for this increased mortality found at autopsy. It is thus important to limit the developing whole body cooling associated with cerebral hypothermia.
Cooling for hypothermic therapy is presently achieved by cold room technology involving a heat exchanger in heart-lung bypass surgery. This kind of surgery takes place in a room the size of a large commercial freezer. Major drawbacks with the cold room technology include that it is invasive and expensive, as a highly skilled team of medical personnel are necessary to operate a standard heart-lung bypass machine. Cooling can also be achieved by using natural or synthetic icepacks. These kinds of methods and devices have drawbacks. The disadvantages with natural and synthetic icepacks include melting, and the cooling temperature cannot be regulated.
U.S. Pat. No. 5,261,339 discloses a device and method for resuscitating the brain as a result of ischemic and anoxic injuries which comprises a head enveloping helmet and a neck supporting back plate with interconnected hollow cavities through which chilled gas form an activated coolant source or cooled liquids pass to chill the brain and upper spinal column. The device is intended for short-term use in the field at a trauma site on persons who have suffered cardiac arrest, respiratory arrest, stroke, suffocation, drowning or similar, to prevent neurologic injury from immediate lack of bloodflow to the brain, or oxygen to the brain, which may occur within minutes of cessation or substantial reduction of blood or oxygen flow.